It is difficult to break through the undocumented format.
#
# things supported by real insets in mathed
#
+#
+# The syntax of lib/symbols is very ad hoc.
+# There are several possible formats of a line, which are quite different.
# decorations
acute decoration none
#end end none
+# In order to use one of the decorations of MathSupport.cpp, the line must
+# be handled by a math inset which calls mathed_draw_deco().
+# If new symbol do not fit into any of the existing insets, it would be ignored
+# and new inset must be programmed.
+# Better solutions is to use the font to draw the symbols as below.
+
#
# symbols generated from fontmath.ltx
#